The book covers this much better than any comment can (and is a breezy read!) But there is absolutely a difference, which you already mentioned: Seat in chair

The book covers this much better than any comment can (and is a breezy read!) But there is absolutely a difference, which you already mentioned: Seat in chair for 8 hrs. They might be spending it watching YouTube but they can't volunteer or start a band or do whatever they want. With UBI there is no nominal expectations so nobody does anti-useful things like adding paperwork to justify their existence. The key part of the book for me is that people really truly want to work and be useful. Case in point why people accept teaching roles despite the bad pay. Even more useful things like firefighters or suicide hotline workers people will volunteer to do for free. Jobs that are useless can't get people to stay for any reason other than money. In essence, it pays well because it is useless. One option (UBI) is to pay everyone and then they do what they feel is most useful. People doing jobs they love will happily continue doing them. More people will be teachers or craftsmen, or artists. Jobs that suck but really need to get done will pay more, because the workers will be comparing it to doing something else and not to starvation. But the incentives for doing useful work are not there, since enough people are willing to be paid in good feelings instead of salary. So if not UBI something needs to change to make real useful jobs worth it